Paper rolls, later referred to simply as rolls, are wrapped in an elastic packaging wrapper, typically a kraftliner or plastic film web, or both. Also conventional is the use of such a wrapper material in which the above-mentioned material elements are laminated together so as to form a so-called "sandwich" wrapper material. The function of the plastic film in the roll wrapper is to provide a moisture barrier for protecting the rolls against ambient humidity, while the kraftliner imparts the required mechanical impact protection during transportation and handling of the rolls as the rolls are, e.g., loaded by clamp lift trucks in the various stages of the shipping process.
For the mechanical handling durability of the packaged roll it is imperative that the wrapper material is applied slacklessly about the roll and it has no "creases" that can initiate a damage in the package through, e.g., sticking of the lift forks in the creases or rubbing of the rolls against each other during transportation. Furthermore, the creases can cause impression marking of the paper web in the roll.
Typically, the paper roll is wrapped in an elastic wrapper material by rotating the paper roll on support rolls and feeding the wrapper as a continuous web by means of a feed nip and conveyors and/or gravitationally into the nip formed between the paper roll and the support rolls, and the leading end of the wrapper is attached to the paper roll, conventionally by adhesive means.
During wrapping, the wrapper is tensioned between the wrapping station and the wrapper feed units in order to obtain a tightly wrapped roll. The wrapper tension is adjusted by controlling the mutual speed difference of the wrapping rolls and the feed nip, and/or braking the rotational speed of the wrapper dispenser unit.
The wrapper material is typically wound by 2 . . . 4 layers about the paper roll, severed by conventional methods and the layers are glued to each other at least at the wrapper trailing end, thus sealing the packaged roll. Finally, the overextending edges of the wrapper are folded with the help of a folding apparatus and the paper roll ends are covered by end headers.
During the wrapping of paper rolls, the wrapper frequently develops creases at which the package is easily severed during handling of the rolls. This problem is accentuated the wider the rolls are. Roll wrappers are often printed with factory logotypes, thus also acting as factory "visiting cards". A creased roll wrapper also looks ugly and thereby acts as bad advertising for the product and factory image.
The above-discussed problem of crease formation originates from the feed of the wrapper leading end into the nip formed between the roll to be wrapped and the rotating support roll, and therefrom further about the roll. The wrapper leading end is cut transversely to the feed direction and frequently is warped on the wrapper payoff roll, thus also easily assuming a warped state when entering the first feed elements. Owing to the above-mentioned warping and bending of the wrapper, the feed of the wrapper leading end by pushing it from behind into the nip between the roll to be wrapped and the rotating support roll is difficult, whereby the wrapper leading end readily enters the nip between the roll to be wrapped and the rotating support rolls in a slightly oblique direction relative to the axial direction of the roll. Moreover, the roll resting on the support rolls also frequently assumes a somewhat axially misaligned position, which further is the origin of the problem described below in greater detail. During the progress of the roll wrapping, the wrapper is tensioned between the rotating support rolls and the feed nip, and/or the wrapper dispenser unit, whereby the oblique alignment of the wrapper leading end and/or the roll to be wrapped causes an uneven and oblique tension in the cross direction of the wrapper web. This oblique tensioning of the elastic wrapper web warps the web in the web tensioning direction into undulations which later are flattened in the nip between the roll to be wrapped and the rotating support rolls into above-mentioned disadvantageous creases on the packaged roll. This effect of crease formation takes place the easier the more pliable the wrapper material. A particularly problematic case of this category is experienced when a so-called "testliner" made from pliable recycled fiber or a plastic film is used.